The present invention relates to an improved method for establishing an airtight seal between the bead of a tubeless tire and a rim, and to an apparatus specially adapted to practice that method. More particularly, the present invention is directed to a bead seating method and apparatus which employs a pneumatic pulse having a leading edge with a short rise time both to impart momentum to the bead and inject air into the tire, and thereby initiate a bead motion which results in the progressive seating thereof.
One of the chief difficulties associated with the changing of tubeless tires is the difficulty of establishing the initial airtight seal between the bead of the tire and the bead-seating surface of the rim on which it is to be mounted. This difficulty results from the fact that, when a tire is uninflated, the open space or gap between its bead and the bead-seating surface of the rim is often so large that seating is prevented by the leakage of air therethrough. The problem is that, at the same time that a large gap renders the tire unable to hold air, the inability of the tire to hold air prevents it from expanding so as to reduce the size of the gap. This problem is most serious in the case of heavy truck tires, particularly radial truck tires, because the stiffness of such tires makes them resistant to forces that tend to reduce the gap sufficiently for seating to occur.
Prior to the present invention a number of different tools have been developed in an attempt to solve the above described problem. One class of such tools, which are best described as mechanical, although they may include some pneumatic elements, rely on the use of flexible straps or segmented hoops which squeeze the tire along the circumference of its tread and thereby force its bead upward toward the bead-seating surface. On example of an apparatus of the former type is described in U.S. Pat. No. 3,578,059, issued to J. Uhen on May 11, 1971. An example of the latter type is described in copending U.S. patent application Ser. No. 07/511,322, filed on Apr. 19, 1990, by S. Ochoa, the inventor of the present invention.
Another class of such tools, which are best described as pneumatic, although they include some non-pneumatic elements, rely on the injection of a narrow jet or on a circular curtain of high pressure air between the bead and the bead-seating surface. One example of a pneumatic seating tool of the former type is described in U.S. Pat. No. 3,866,654, issued to V. Duquesne on Feb. 18, 1975. Examples of pneumatic seating tools of the latter type include U.S. Pat. Nos. 3,522,469, issued to L. Corless on Jan. 5, 1971, and 3,683,991, issued to F. Ruhland et al. on Aug. 15, 1972.
While pneumatic seating tools of the above-mentioned types are able to seat many of the more easily seated types of tires, such as automobile tires, they have limitations or disadvantages which prevent their being used successfully on heavy truck tires or on tires that are badly collapsed, i.e., which have unusually large tire-rim gaps when in their uninflated condition. For pneumatic seating tools of the type which inject a circular curtain of air into the tire-rim gap, one of these is that their structure inherently limits their use to tires of a single size. This is because the diameter of the curtain of air must match the diameter of the bead of the tire. Another of these is that their method of operation limits their use to tires which have a horizontal orientation. This is because only a horizontal orientation allows the weight of the tire to produce the symmetrical tire-rim gap which allows air to enter that gap from all directions at once. Finally, such tools may require the use of air pressures which far exceed the pressure (125 psi) that is considered to be the safe maximum for general purpose vehicular applications.
Pneumatic seating tools of the type which inject a narrow jet of air into the tire-rim gap exhibit a different but equally limiting range of disadvantages. One of these is that they often fail to seat tires which are heavy or badly collapsed, even when the tires have the orientation (i.e., horizontal) in which they are most easily seated. Another is that the highest probability of a successful seating is achieved when the injection nozzle is positioned between the tire and the rim, a position which can easily cause the nozzle to be trapped therebetween, thereby preventing the seating process from running to completion. Finally, such tools may also require the use of pressures which exceed those considered safe for general purpose vehicular applications.